This application claims priority from German patent Application No. 201 07 778.7, titled PUNCTURE CANNULA, filed in Germany on May 8, 2001, the entire contents of which is incorporated by reference herein as though set forth in full.
The instant invention relates to a puncture cannula, particularly for nerve stimulation, comprising a steel cannula attached to a cannula hub and a cable extending through an insertion channel of the cannula hub and having a core connected to the steel cannula.
European Patent 0 102 538 B1 discloses a puncturing and catheterizing device which is suited for the puncturing and catheterizing of nerve strings. This device comprises a steel cannula with a cannula hub provided at the distal end of the cannula. The steel cannula is connected to a cable by which an electric potential can be applied to the steel cannula. When the steel cannula, which has an exposed tip, is brought into a position close to a nerve, electrical pulses, which are applied to the cable by a suitable stimulation device, will cause a nerve stimulation, resulting in corresponding reflexes of the patient. In this manner, it can be verified whether the tip of the cannula has been guided sufficiently close to the selected nerve. Thereafter, an anesthetic agent can be injected either through the cannula or through a catheter which has been set by use of the cannula in order to perform local anesthesia. In the known device, the electrical connection of the core of the cable to the steel cannula is performed by winding the core around the cannula, or by soldering the core to the cannula and subsequently enmolding the connection. Such a connection technique is complicated and overly expensive.
It is an object of the invention to provide a puncture cannula which is easily manufactured and guarantees a safe contact between the cable and the puncture cannula.
According to the instant invention, the hub of the cannula comprises a metallic clamping element which is formed with a first clamping slot for engaging the steel cannula and with a second clamping slot for engaging the core of the cable. By insertion of the clamping element into the hub of the cannula, the steel cannula and the core of the cable will be automatically positioned in their respective clamping slot to be tightly surrounded therein. In this manner, these two components are clamped into their desired positions at the same time, while the clamping of one component will not be affected by the other component. The clamping element is provided as a one-piece member, with its clamping slots arranged in such a configuration that the first clamping slot clamps the steel cannula when the second clamping slot clamps the core of the cable. Thus, the clamping slots have the same mutual distance as the steel cannula and the core of the cable and will be activated by displacing the clamping element.
A considerable advantage of the invention resides in the simple and safe mounting process. By displacement of the clamping member, the steel cannula and the cable are fixed relative to each other and are also fixed relative to the hub of the cannula. It is also possible to perform the clamping prior to the attaching of the steel cannula in the hub of the cannula. In this case, an adhesive is inserted into a recess of the cannula hub after insertion of the clamping element. This adhesive will enter into all gaps to thus fasten the steel cannula in the hub of the cannula. Further, the adhesive serves as a surrounding electrical shielding for the cable and lends further stability the fixation of the cable. Further, the adhesive fulfills the function to cover all metallic parts which exist on or in the hub of the cannula, thus precluding the possibility that a person might inadvertently come into contact with any one of the current-carrying parts.
According to a preferred embodiments of the invention, it is provided that the second clamping slot is formed with cutting edges adapted to penetrate an insulation of the cable. This obviates the need to first strip the cable and expose the core of the cable. When the clamping element is inserted into the hub of the cannula, the cutting of the cable insulation and the clamping of the core of the cable are performed automatically in the process.
Preferably, the clamping slots are arranged behind each other in the clamping element, with a converging opening provided between the clamping slots so as to decouple the two clamping slots from each other.
The puncture cannula of the invention is particularly suited for nerve stimulation. The instant puncture cannula is compatible with different techniques for using a cannula. Thus, for instance, an anesthetic agent can be injected directly through the steel cannula, or the steel cannula can be connected to a short catheter or a capillary tube. It is also possible to set a catheter via the puncture channel generated by the steel cannula, either with or without a guide wire.
The clamping element can be of a design adapted to various diameters of steel cannulae and/or of cores of cables.
A preferred embodiment of the invention will be described in greater detail hereunder with reference to the accompanying drawings.